Technical Abstract:
The effects of compost and biological amendments on soil fertility, soil microbial communities, soil-borne diseases, insect pests and potato yield quality and quantity were assessed at two farm sites in Northern Maine in 2007. The two sites were: Aroostook Farm (AF), a research farm using conventional production practices, and Wood Prairie Farm (WP), a commercial organic farm. Biological amendments consisted of one of three different biocontrol agents, hypovirulent Rhizoctonia solani Rhs 1A1 (HvRs), Bacillus subtilis (Bsub), and Trichoderma virens (Tvir), added to plots with and without a conifer-based (Hemlock bark) compost amendment, in addition to a non-amended control. At Aroostook Farm, the compost amendment reduced incidence and severity of black scurf by 12-27%, and increased tuber yields by 13-23%. Biocontrol treatments (Tvir and HvRs) reduced incidence and severity of black scurf by 9-31% but had no significant effect on yield. The combined effect of compost and biocontrol amendments reduced black scurf by 30-48% and increased yield. At Wood Prairie Farm, where soil was already rich in organic matter, compost did not significantly reduce scurf or scab but nonetheless increased tuber yield (9-30%). Biocontrol treatments (Tvir and Bsub) reduced incidence and severity of black scurf by 10-48%, scab by 5-20%, and the total of all diseases by 15-30%. Better soil quality at the organic farm site (high organic matter, soil moisture, microbial populations & activity) resulted in overall lower disease and higher yields. Appropriate compost and biological amendments had significant positive effects on soil quality, disease reduction, and yield, and should play an important role in sustainable soil and disease management programs.